﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  

  

  33 
  

  

  Table 
  6 
  

   Mode 
  of 
  gabbro 
  

  

  Units 
  

   measured 
  

  

  Rel. 
  vols. 
  

  

  S. 
  G. 
  

  

  Units 
  by 
  Percentage 
  

  

  weight 
  weights 
  

  

  Plagioclase 
  . 
  . 
  

   Orthoclase. 
  . 
  

   Hornblende 
  . 
  

   Hypersthene 
  

  

  Biotite 
  

  

  Augite 
  

  

  Garnet 
  

  

  Ilmenite. 
  . 
  . 
  . 
  

  

  Pyrite 
  

  

  Apatite 
  

  

  2 
  805 
  

  

  335 
  

   1 
  990 
  

  

  932 
  

   505 
  

   227 
  

   265 
  

   184 
  

  

  95 
  

   26 
  

  

  38 
  

   4 
  

   27 
  

   12 
  

   6 
  

   3 
  

   3 
  

   2 
  

   1 
  

  

  09 
  

  

  2 
  

  

  55 
  

  

  2 
  

  

  02 
  

  

  3 
  

  

  65 
  

  

  3 
  

  

  86 
  

  

  3 
  

  

  08 
  

  

  3 
  

  

  59 
  

  

  3 
  

  

  50 
  

  

  5 
  

  

  29 
  

  

  5 
  

  

  35 
  

  

  3 
  

  

  7 
  461 
  

   858 
  

   5 
  368 
  

   3 
  262 
  

   1 
  616 
  

  

  749 
  

  

  980 
  

  

  95i 
  

  

  475 
  

   83 
  

  

  7 
  364 
  

  

  99.98 
  

  

  22 
  803 
  

  

  100.00 
  

  

  Under 
  the 
  old 
  qualitative 
  system 
  the 
  rock 
  is 
  a 
  hornblende 
  norite, 
  

   while 
  according 
  to 
  the 
  quantitative 
  system 
  it 
  is 
  a 
  hornblende-camp- 
  

   tonose. 
  In 
  thin-section 
  the 
  plagioclase 
  is 
  seen 
  to 
  range 
  from 
  oligo- 
  

   clase 
  to 
  labradorite, 
  and 
  the 
  analysis 
  and 
  mode 
  show 
  that 
  the 
  average 
  

   composition 
  is 
  that 
  of 
  a 
  basic 
  andesine. 
  The 
  high 
  Ti0 
  2 
  of 
  the 
  an- 
  

   alysis 
  shows 
  either 
  ilmenite 
  or 
  very 
  titaniferous 
  magnetite, 
  the 
  

   ilmenite 
  being 
  far 
  more 
  probable 
  because 
  of 
  the 
  difficulty 
  of 
  other- 
  

   wise 
  accounting 
  for 
  such 
  a 
  low 
  content 
  of 
  Fe 
  a 
  3 
  . 
  

  

  